This invention relates generally to the field of dishwashers and more particularly to an improved thermoplastic wash arm therefore which includes heat shielding apparatus for protecting the thermoplastic wash arm from deformation due to heat during the dish drying portion of a cycle of operations.
Automatic dishwashers of the type which pump washing liquid through rotatable wash arms for distribution within a washing chamber to wash articles placed therein have traditionally utilized wash arms manufactured from stainless steel material. A potential reduction in manufacturing costs can be realized if these wash arms are manufactured from a thermoplastic material. One of the wash arms is usually positioned slightly above the bottom wall of the washing chamber for spraying liquid upwardly onto articles held in a basket. Since dishwashers generally utilize a sheathed electrical heater for heating washing liquid and for heating the washing chamber to dry the washed articles there exists the potential problem that a lower plastic wash arm could be deformed by the radiant heat emitted by the electrical heater.
As a result of this potential problem and a reluctance to design away from a sheathed heater within the washing chamber there has been little movement toward the use of a thermoplastic lower wash arm in a dishwasher. One manufacturer, however utilizes both a thermoplastic washing chamber and a thermoplastic lower wash arm while retaining the sheathed electrical heater mounted to the bottom wall of the washing chamber. In this construction, the electrical heater is designed as a dual wattage element which utilizes a relatively high wattage when the heater is covered with liquid and a relatively low wattage when the heater is exposed to air for drying washed articles. The temperatures adjacent the plastic wash arm are maintained at a low level because of the low wattage of the heater for preventing heat damage to the wash arm. In addition, the heater is an elongated member of relatively low watt density.
While not utilized in a dishwasher having a plastic wash arm, U.S. Pat. No. 3,555,242 shows a generally tubular metal shield surrounding the heater. The tubular shield acts as a secondary heating surface of greater area and lower temperature than the surface of the heater.
In U.S. Pat. No. 4,096,872 a dishwasher having a thermoplastic washing chamber or tub is disclosed. The bottom wall of the washing chamber adjacent the heating element includes a plurality of fluid retaining receptacles. These receptacles retain washing liquid which is evaporated during the drying portion of the cycle to maintain the bottom wall at a safe operating temperature.
While it is noted that a dishwasher having a lower thermoplastic wash arm has been shown and that a metal shield has been shown surrounding a dishwasher heating element, there has been no known showing of a dishwasher which utilizes a thermoplastic lower wash arm having a heat dissipating shield attached thereto. The heat shielded lower thermoplastic wash arm is thus usable with a high wattage heater without the need for a thermostat to limit temperature or a rectifier to limit the wattage of the heater when in the drying portion of a cycle of operations.